Home Forums Reloading Big Game Rifles Temp sensitivity?

I worked up a load for my 7 SAUM with RL22 at Nosler's listed max. There wasn't any bolt lift issues or brass and primer issues that showed over pressure. The temp at the time of testing was 80-85 degrees. Should I expect to see any issues when hunting season comes in this fall/winter from this load? I'm not familiar with temp sensitivity, so I thought I would ask the experts.

Thanks.

How cold might the temperature get? I haven't experienced problems with RL-22 until down around zero Fahrenheit.

Probably no lower than around 20 degrees or so. Also, I'll be hunting at 9,000' vs 300' where the load was developed. If any of that matters.

What I have seen SOMETIMES when testing loads down around zero is point of impact at 100 yards can shift up to 3 inches in any direction with powders that lose significant velocity. That much isn't common--I've only seen it in two rifles and load over the years--but 1-2 inches is pretty common. This obviously isn't much at 100 yards, but 2 inches at 100 amounts to 6 inches at 300 and 8 inches at 400.

This shifting POI usually occurs in fairly light-barreled rifles that also show noticeable shift in POI when increasing powder charges while working up loads. Heavier barrels reduce this tendency, but I have never seen more than 1 inch in POI shift from 70 to zero degrees with a powder that loses less than 50 fps. It's common with powders that lose 75 to over 100 fps, but still doesn't necessarily happen with all rifles. The MOST velocity I've seen a big game load lose was 176 fps, but even that load only shifted an inch in POI at zero degrees.

Elevation is a separate issue. It changes downrange POI by increasing the amount of retained velocity. You can find a good approximation of the effect it will have by using one of the many free ballistic programs on the Internet, if you don't have one on your cell phone.

Thank you, sir, for the info and your time. Increases in pressure and loss of accuracy was my main concerns. I'll be checking my zero once I get out there, so a POI shift hopefully won't be a big deal.

I'm new to reloading and this will be my first trip with only my reloads. So, I'm a little nervous.


Thanks again.

If the temps are cooler by a significant amount (say, 30 or more degrees) you will probably see a lessening of the velocity and a change in your grouping. How much varies by powder, cartridge and charge.
I had a decent load in a 25-06 with RL19 that I developed in temps of around 40-45 degrees. When the temps hit 90, the load was too hot with extractor marks and hard lift on the bolt.

Suppose you tried 54, 55, 56, and 57 grains of some powder that is temp sensitive, at 95 degrees F, and the 57-grain charge made you a tackdriver load...and the others sucked. Suppose the change in velocity for each grain of powder is 75 fps.

Then suppose you find that at 45 degrees F, your 57-grain tackdriver load is giving you 150 fps less just like 55 grains of power did at 95 degrees F.

My question is: why wouldn't you expect the same accuracy you got with 55 grains when you were developing the load when you shoot the 57-grain load at 45 degrees F?

I have never carried out the experimentation to find the answer but I'd be surprised if no one knows (and I do mean REALLY KNOWS and not just believes) the answer.

My guess is that at 45 degrees, the load would suck just like the 55-grain load did at 95 degrees F.

So...what does anyone know?

I have done a bunch of ammo-testing at various temperatures from around zero to 95. At 95 I sometimes "greenhouse" the ammo in a clear Ziplock bag set in the sun with a small thermometer until the temperature's 115-120--and I leave the rifle in the sun too, to heat up as much as possible. Sometimes I'll shoot a number of rounds as fast as they can be aimed well, to heat up the barrel. In the cold tests everything is at ambient temperature, kept in an unheated garage overnight before the test to make sure.

Sometimes accuracy and point of impact stay the same, and sometimes they don't. But there is no definite pattern, except that the less variation in velocity at different temperatures the less likely variations in accuracy and point of impact are like to occur.

Thanks John...I sure like having you around!

I am focused on this, which I think tends to support my theoretical conclusion.: